An anesthetic metering device of the above-described class has become known from EP-A2-231,513. The prior-art anesthetic metering device consists of a reservoir, from which liquid anesthetic is pressed by a delivery pressure into a heated vaporizer chamber serving as an anesthetic vapor source. The pressurized anesthetic vapor is metered via a cyclically operating metering valve into a carrier gas stream, e.g., an oxygen-laughing gas mixture, and sent to an anesthetic apparatus. Corresponding to the pressure in the vaporizer chamber, the degree of opening of the metering valve, and the volume flow of the carrier gas per unit time, a corresponding anesthetic concentration becomes established in the carrier gas stream.
One disadvantage of the prior-art anesthetic metering device is the fact that if the heating of the vaporizer chamber is insufficient, e.g., in the case of malfunction of the heater, liquid anesthetic may enter the carrier gas stream, leading to a considerable increase in concentration there.
Malfunction of the metering valve would also cause an abrupt entry of the anesthetic vapor present in the vaporizer chamber into the carrier gas stream. Another disadvantage is the fact that the delivery pressure in the reservoir is difficult to set to a stable value in the case of low-boiling anesthetics, as a result of which the volume of liquid anesthetic flowing per unit time into the vaporizer chamber is subject to variations, because the vapor pressure acts in addition to the delivery pressure.
An anesthetic metering device known from DE-C2,31,16,951 provides for delivery of liquid anesthetic with a pump from a reservoir into a heated vaporizer chamber, where it is completely mixed into the carrier gas stream flowing through the vaporizer chamber.
One disadvantage of the prior-art device is the fact that an increased amount of liquid anesthetic enters the vaporizer chamber in the case of malfunction of the pump, and leads to an uncontrolled increase in the anesthetic concentration in the carrier gas stream there.